Arsenic oxidation and bioaccumulation by the acidophilic protozoan, Euglena mutabilis, in acid mine drainage (Carnoulès, France)

Exploring Extremotolerant and Extremophilic Microalgae: New Frontiers in Sustainable Biotechnological Applications

Exploring extremotolerant and extremophilic microalgae opens new frontiers in sustainable biotechnological applications. These microorganisms thrive in extreme environments and exhibit specialized metabolic pathways, making them valuable for various industries. The study focuses on the ecological adaptation and biotechnological potential of these microalgae, highlighting their ability to produce bioactive compounds under stress conditions. The literature reveals that extremophilic microalgae can significantly enhance biomass production, reduce contamination risks in large-scale systems, and produce valuable biomolecules such as carotenoids, lipids, and proteins. These insights suggest that extremophilic microalgae have promising applications in food, pharmaceutical, cosmetic, and biofuel industries, offering sustainable and efficient alternatives to traditional resources. The review concludes that further exploration and utilization of these unique microorganisms can lead to innovative and environmentally friendly solutions in biotechnology.

Euglena mutabilis exists in a FAB consortium with microbes that enhance cadmium tolerance

BACKGROUND

Synthetic algal-fungal and algal-bacterial cultures have been investigated as a means to enhance the technological applications of the algae. This inclusion of other microbes has enhanced growth and improved stress tolerance of the algal culture. The goal of the current study was to investigate natural microbial consortia to gain an understanding of the occurrence and benefits of these associations in nature. The photosynthetic protist Euglena mutabilis is often found in association with other microbes in acidic environments with high heavy metal (HM) concentrations. This may suggest that microbial interactions are essential for the protist's ability to tolerate these extreme environments. Our study assessed the Cd tolerance of a natural fungal-algal-bacterial (FAB) association whereby the algae is E. mutabilis.

RESULTS

This study provides the first assessment of antibiotic and antimycotic agents on an E. mutabilis culture. The results indicate that antibiotic and antimycotic applications significantly decreased the viability of E. mutabilis cells when they were also exposed to Cd. Similar antibiotic treatments of E. gracilis cultures had variable or non-significant impacts on Cd tolerance. E. gracilis also recovered better after pre-treatment with antibiotics and Cd than did E. mutabilis. The recoveries were assessed by heterotrophic growth without antibiotics or Cd. In contrast, both Euglena species displayed increased chlorophyll production upon Cd exposure. PacBio full-length amplicon sequencing and targeted Sanger sequencing identified the microbial species present in the E. mutabilis culture to be the fungus Talaromyces sp. and the bacterium Acidiphilium acidophilum.

CONCLUSION

This study uncovers a possible fungal, algal, and bacterial relationship, what we refer to as a FAB consortium. The members of this consortium interact to enhance the response to Cd exposure. This results in a E. mutabilis culture that has a higher tolerance to Cd than the axenic E. gracilis. The description of this interaction provides a basis for explore the benefits of natural interactions. This will provide knowledge and direction for use when creating or maintaining FAB interactions for biotechnological purposes, including bioremediation.

The biomolecules of Euglena gracilis: Harnessing biology for natural solutions to future problems

Over the past decade, the autotrophic and heterotrophic protist Euglena gracilis (E. gracilis) has gained popularity across the studies of environmental science, biosynthesis experiments, and nutritional substitutes. The unique physiology and versatile metabolism of E. gracilis have been a recent topic of interest to many researchers who continue to understand the complexity and possibilities of using E. gracilis biomolecule production. In this review, we present a comprehensive representation of recent literature outlining the various uses of biomolecules derived from E. gracilis across the fields of natural product biosynthesis, as a nutritional substitute, and as bioremediation tools. In addition, we highlight effective strategies for altering metabolite production using abiotic stressors and growth conditions. To better understand metabolite biosynthesis and its role in E. gracilis, integrated studies involving genomics, metabolomics, and proteomics should be considered. Together, we show how the ongoing advancements in E. gracilis related research continue to broaden applications in the biosynthetic sector and highlight future works that would strengthen our understanding of overall Euglena metabolism.

The impact of elevated sulfur and nitrogen levels on cadmium tolerance in Euglena species

Heavy metal (HM) pollution threatens human and ecosystem health. Current methods for remediating water contaminated with HMs are expensive and have limited effect. Therefore, bioremediation is being investigated as an environmentally and economically viable alternative. Freshwater protists Euglena gracilis and Euglena mutabilis were investigated for their tolerance to cadmium (Cd). A greater increase in cell numbers under Cd stress was noted for E. mutabilis but only E. gracilis showed an increase in Cd tolerance following pre-treatment with elevated concentrations of S or N. To gain insight regarding the nature of the increased tolerance RNA-sequencing was carried out on E. gracilis. This revealed transcript level changes among pretreated cells, and additional differences among cells exposed to CdCl2. Gene ontology (GO) enrichment analysis reflected changes in S and N metabolism, transmembrane transport, stress response, and physiological processes related to metal binding. Identifying these changes enhances our understanding of how these organisms adapt to HM polluted environments and allows us to target development of future pre-treatments to enhance the use of E. gracilis in bioremediation relating to heavy metals.

Microbial communities from weathered outcrops of a sulfide-rich ultramafic intrusion, and implications for mine waste management

The Duluth Complex (DC) contains sulfide-rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally-weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long-term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally-weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse uncultured Ktedonobacteria, Acetobacteria, and Actinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally-weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide-rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large-scale mining operations.

Molecular structures of dissolved and colloidal AsV-FeIII complexes and their roles in the mobilization of AsV under strongly acidic conditions

The effect of high concentration of iron (Fe^III) on the speciation and mobility of arsenic (As) under strongly acidic conditions remains unclear. This work studied the redistribution and speciation of As^V and Fe^III at Fe/As molar ratio of 1-14 and pH 1.5-2.0 in the dissolved, colloidal, and solid phases. Results showed that the elevated Fe^III induced the decomposition of the precipitated poorly crystalline ferric arsenate by forming dissolved (< 3 kDa) and colloidal (3 kDa-0.1 µm) As-Fe complexes. The fraction of particulate As (> 0.1 µm) decreased from 70-90% to less than 20% when the Fe/As molar ratio increased from 1 to 14. The particle size of the bulk samples decreased significantly with the increase of Fe^III concentration. The FTIR results suggested that As^V in dissolved/colloidal As-Fe complexes dominantly occurred as HAsO₄^2- species. The EXAFS results indicated that each HAsO₄^2- coordinated with approximately two Fe atoms in dissolved/colloidal As-Fe complexes at Fe/As ≥ 2. The findings suggest that high aqueous Fe^III concentration can promote the mobility of As by forming dissolved/colloidal Fe-As complexes in acidic waters, potentially accelerating As transport from source to downstream in acid mine drainage systems.

Ubiquity of Euglena mutabilis Population in Three Ecologically Distinct Acidic Habitats in Southwestern Japan

Three strains of Euglena mutabilis were isolated from sediments in acidic inland water systems (pH = 3.4–4.7), in Southwestern Japan—acid mine drainage in Sensui (Fukuoka), cold sulfidic spring in Bougatsuru (Oita), and a temporal pool in the Ebinokogen volcanic area (Miyazaki). All strains grew well in acidic media at pH 3.07. Phylogenetic analysis among these three strains showed high similarities to plastid SSU and nuclear SSU rRNA gene sequences (99.86% and 99.76%, respectively). They were closely related to the cultured isolates from other highly acidic habitats (pH = 2.0–5.9). Concentration of sulfate, aluminum, calcium, and iron had 7–70 fold of differences among the three studied habitats. Our results imply that the rRNA genes of E. mutabilis have compensated for their low genetic diversity by adapting to a wide pH range, as well as various water chemistry of habitats.

Toxicity, Physiological, and Ultrastructural Effects of Arsenic and Cadmium on the Extremophilic Microalga Chlamydomonas acidophila

The cytotoxicity of cadmium (Cd), arsenate (As(V)), and arsenite (As(III)) on a strain of Chlamydomonas acidophila, isolated from the Rio Tinto, an acidic environment containing high metal(l)oid concentrations, was analyzed. We used a broad array of methods to produce complementary information: cell viability and reactive oxygen species (ROS) generation measures, ultrastructural observations, transmission electron microscopy energy dispersive x-ray microanalysis (TEM-XEDS), and gene expression. This acidophilic microorganism was affected differently by the tested metal/metalloid: It showed high resistance to arsenic while Cd was the most toxic heavy metal, showing an LC₅₀ = 1.94 µM. Arsenite was almost four-fold more toxic (LC₅₀= 10.91 mM) than arsenate (LC₅₀ = 41.63 mM). Assessment of ROS generation indicated that both arsenic oxidation states generate superoxide anions. Ultrastructural analysis of exposed cells revealed that stigma, chloroplast, nucleus, and mitochondria were the main toxicity targets. Intense vacuolization and accumulation of energy reserves (starch deposits and lipid droplets) were observed after treatments. Electron-dense intracellular nanoparticle-like formation appeared in two cellular locations: inside cytoplasmic vacuoles and entrapped into the capsule, around each cell. The chemical nature (Cd or As) of these intracellular deposits was confirmed by TEM-XEDS. Additionally, they also contained an unexpected high content in phosphorous, which might support an essential role of poly-phosphates in metal resistance.

Remediation of Potential Toxic Elements from Wastes and Soils: Analysis and Energy Prospects

The aim of this study is to evaluate the application of the main hazardous waste management techniques in mining operations and in dumping sites being conscious of the inter-linkages and inter-compartment of the contaminated soils and sediments. For this purpose, a systematic review of the literature on the reduction or elimination of different potential toxic elements was carried out, focusing on As, Cd and Hg as main current contaminant agents. Selected techniques are feasible according to several European countries’ directives, especially in Spain. In the case of arsenic, we verified that there exists a main line that is based on the use of iron minerals and its derivatives. It is important to determine its speciation since As (III) is more toxic and mobile than As (V). For cadmium (II), we observed a certain predominance of the use of biotic techniques, compared to a variety of others. Finally, in mercury case, treatments include a phytoremediation technique using Limnocharis flava and the use of a new natural adsorbent: a modified nanobiocomposite hydrogel. The use of biological treatments is increasingly being studied because they are environmentally friendly, efficient and highly viable in both process and energy terms. The study of techniques for the removal of potential toxic elements should be performed with a focus on the simultaneous removal of several metals, since in nature they do not appear in isolation. Moreover, we found that energy analysis constitutes a limiting factor in relation to the feasibility of these techniques.

Complexation of Eu(III), Pb(II), and U(VI) with a Paramecium glycoprotein: Microbial transformation of heavy elements in the aquatic environment

This study investigated the interaction of inorganic aqueous Eu(III), Pb(II), and U(VI) with Paramecium sp., a representative single-celled protozoan that lives in freshwater. Living and prekilled Paramecium cells were tested. The prekilled cells were killed with a fixative. After 24 h exposure of the cells to inorganic aqueous solutions containing Eu(III) or U(VI), analyses by microparticle-induced X-ray emission with a focused beam (<1 μm) did not detect Eu and U in the living cells, whereas Eu and U were detected in the prekilled cells. Size exclusion chromatography coupled with on-line ultraviolet-visible detection and elemental detection by inductively coupled plasma mass spectrometry of the aqueous phases collected after the living cell experiments revealed that a fraction of the Eu, Pb, and U in the aqueous phase bound to a large (ca. 250 kDa) Paramecium biomolecule and formed a metal-organic complex. The characteristics of the biomolecule were consistent with those of the soluble glycoproteins covering the surfaces of Paramecium cells. These results show that Paramecium cells transform inorganic aqueous Eu, Pb, and U to organic complexes. This paper discusses the relation between this novel complexation and the sorption of these heavy elements on Paramecium cells.

Microbially mediated aluminosilicate formation in acidic anaerobic environments: A cell-scale chemical perspective

Through the use of scanning transmission electron microscopy (STEM) combined with other complementary techniques (SEM, cryo-TEM, HRTEM, and EELS), we have studied the interaction of microorganisms inhabiting deep anoxic waters of acidic pit lakes with dissolved aluminum, silica, sulfate, and ferrous iron. These elements were close to saturation (Al, SiO₂ ) or present at very high concentrations (0.12 m Fe(II), 0.12-0.22 m SO₄^2- ) in the studied systems. The anaerobic conditions of these environments allowed investigation of geomicrobial interactions that are difficult to see in oxidized, Fe(III)-rich environments. Detailed chemical maps and through-cell line scans suggest both extra- and intracellular accumulation of Al, Si, S, and Fe(II) in rod-like cells and other structures (e.g., spherical particles and bacteriomorphs) of probable microbial origin. The bacterial rods showed external nanometric coatings of adsorbed Fe(II) and Al on the cell surface and cell interiors with significant presence of Al, Si, and S. These microbial cells coexist with spherical particles showing similar configuration (Fe(II) external coatings and [Al, Si, S]-rich cores). The Al:Si and Al:S ratios and the good Al-Si correlation in the cell interiors suggest the concurrent formation of two amorphous phases, namely a proto-aluminosilicate with imogolite-like composition and proto-hydrobasaluminite. In both cases, the mineralization appears to comprise two stages: a first stage of aluminosilicate and Al-hydroxysulfate precipitation within the cell or around cellular exudates, and a second stage of SO₄^2- and Fe(II) adsorption on surface sites existing on the mineral phases in the case of (SO₄^2- ) or on presumed organic molecules [in the case of Fe(II)]. These microbially related solids could have been formed by permineralization and mineral replacement of senescent microbial cells. However, these features could also denote biomineralization by active bacterial cells as a detoxification mechanism, a possibility which should be further explored. We discuss the significance of the observed Al/microbe and Si/microbe interactions and the implications for clay mineral formation at low pH.

Biochemistry and Physiology of Heavy Metal Resistance and Accumulation in Euglena

Free-living microorganisms may become suitable models for removal of heavy metals from polluted water bodies, sediments, and soils by using and enhancing their metal accumulating abilities. The available research data indicate that protists of the genus Euglena are a highly promising group of microorganisms to be used in bio-remediation of heavy metal-polluted aerobic and anaerobic acidic aquatic environments. This chapter analyzes the variety of biochemical mechanisms evolved in E. gracilis to resist, accumulate and remove heavy metals from the environment, being the most relevant those involving (1) adsorption to the external cell pellicle; (2) intracellular binding by glutathione and glutathione polymers, and their further compartmentalization as heavy metal-complexes into chloroplasts and mitochondria; (3) polyphosphate biosynthesis; and (4) secretion of organic acids. The available data at the transcriptional, kinetic and metabolic levels on these metabolic/cellular processes are herein reviewed and analyzed to provide mechanistic basis for developing genetically engineered Euglena cells that may have a greater removal and accumulating capacity for bioremediation and recycling of heavy metals.

Spatial Distribution of Eukaryotic Communities Using High-Throughput Sequencing Along a Pollution Gradient in the Arsenic-Rich Creek Sediments of Carnoulès Mine, France

Microscopic eukaryotes play a key role in ecosystem functioning, but their diversity remains largely unexplored in most environments. To advance our knowledge of eukaryotic microorganisms and the factors that structure their communities, high-throughput sequencing was used to characterize their diversity and spatial distribution along the pollution gradient of the acid mine drainage at Carnoulès (France). A total of 16,510 reads were retrieved leading to the identification of 323 OTUs after normalization. Phylogenetic analysis revealed a quite diverse eukaryotic community characterized by a total of eight high-level lineages including 37 classes. The majority of sequences were clustered in four main groups: Fungi, Stramenopiles, Alveolata and Viridiplantae. The Reigous sediments formed a succession of distinct ecosystems hosting contrasted eukaryotic communities whose structure appeared to be at least partially correlated with sediment mineralogy. The concentration of arsenic in the sediment was shown to be a significant factor driving the eukaryotic community structure along this continuum.

The Chloroplast Genome of Euglena mutabilis-Cluster Arrangement, Intron Analysis, and Intrageneric Trends

A comparative analysis of the chloroplast genome of Euglena mutabilis underlined a high diversity in the evolution of plastids in euglenids. Gene clusters in more derived Euglenales increased in complexity with only a few, but remarkable changes in the genus Euglena. Euglena mutabilis differed from other Euglena species in a mirror-inverted arrangement of 12 from 15 identified clusters, making it very likely that the emergence at the base of the genus Euglena, which has been considered a long branch artifact, is truly a probable position. This was corroborated by many similarities in gene arrangement and orientation with Strombomonas and Monomorphina, rendering the genome organization of E. mutabilis in certain clusters as plesiomorphic feature. By RNA analysis exact exon-intron boundaries and the type of the 77 introns identified were mostly determined unambiguously. A detailed intron study of psbC pointed at two important issues: First, the number of introns varied even between species, and no trend from few to many introns could be observed. Second, mat1 was localized in Eutreptiales exclusively in intron 1, and mat2 was not identified. With the emergence of Euglenaceae in most species, a new intron containing mat2 inserted in front of the previous intron 1 and thereby became intron 2 with mat1.

Bio-recovery of non-essential heavy metals by intra- and extracellular mechanisms in free-living microorganisms

Free-living microorganisms may become suitable models for recovery of non-essential and essential heavy metals from wastewater bodies and soils by using and enhancing their accumulating and/or leaching abilities. This review analyzes the variety of different mechanisms developed mainly in bacteria, protists and microalgae to accumulate heavy metals, being the most relevant those involving phytochelatin and metallothionein biosyntheses; phosphate/polyphosphate metabolism; compartmentalization of heavy metal-complexes into vacuoles, chloroplasts and mitochondria; and secretion of malate and other organic acids. Cyanide biosynthesis for extra-cellular heavy metal bioleaching is also examined. These metabolic/cellular processes are herein analyzed at the transcriptional, kinetic and metabolic levels to provide mechanistic basis for developing genetically engineered microorganisms with greater capacities and efficiencies for heavy metal recovery, recycling of heavy metals, biosensing of metal ions, and engineering of metalloenzymes.

Spatio-Temporal Detection of the Thiomonas Population and the Thiomonas Arsenite Oxidase Involved in Natural Arsenite Attenuation Processes in the Carnoulès Acid Mine Drainage

The acid mine drainage (AMD) impacted creek of the Carnoulès mine (Southern France) is characterized by acid waters with a high heavy metal content. The microbial community inhabiting this AMD was extensively studied using isolation, metagenomic and metaproteomic methods, and the results showed that a natural arsenic (and iron) attenuation process involving the arsenite oxidase activity of several Thiomonas strains occurs at this site. A sensitive quantitative Selected Reaction Monitoring (SRM)-based proteomic approach was developed for detecting and quantifying the two subunits of the arsenite oxidase and RpoA of two different Thiomonas groups. Using this approach combined with FISH and pyrosequencing-based 16S rRNA gene sequence analysis, it was established here for the first time that these Thiomonas strains are ubiquitously present in minor proportions in this AMD and that they express the key enzymes involved in natural remediation processes at various locations and time points. In addition to these findings, this study also confirms that targeted proteomics applied at the community level can be used to detect weakly abundant proteins in situ.

Anabaena sp. mediated bio-oxidation of arsenite to arsenate in synthetic arsenic (III) solution: Process optimization by response surface methodology

Blue green algae Anabaena sp. was cultivated in synthetic arsenite solution to investigate its bio-oxidation potential for arsenic species. Response surface methodology (RSM) was employed based on a 3-level full factorial design considering four factors, viz. initial arsenic (III) concentration, algal dose, temperature and time. Bio-oxidation (%) of arsenic (III) was considered as response for the design. The study revealed that about 100% conversion of As (III) to As (V) was obtained for initial As (III) concentration of 2.5-7.5 mg/L at 30 °C for 72 h of exposure using 3 g/L of algal dose signifying a unique bio-oxidation potential of Anabaena sp. The dissolved CO2 (DCO2) and oxygen (DO) concentration in solution was monitored during the process and based on the data, a probable mechanism was proposed wherein algal cell acts like a catalytic membrane surface and expedites the bio-oxidation process. Bioaccumulation of arsenic, as well as, surface adsorption on algal cell was found considerably low. Lipid content of algal biomass grown in arsenite solution was found slightly lower than that of algae grown in synthetic media. Toxicity effects on algal cells due to arsenic exposure were evaluated in terms of comet assay and chlorophyll a content which indicated DNA damage to some extent along with very little decrease in chlorophyll a content. In summary, the present study explored the potential application of Anabaena sp. as an ecofriendly and sustainable option for detoxification of arsenic contaminated natural water with value-added product generation.

Effects of nitrogen and phosphorus on arsenite accumulation, oxidation, and toxicity in Chlamydomonas reinhardtii

We studied arsenite (iAs(III)) accumulation, oxidation, and toxicity in the freshwater green alga Chlamydomonas reinhardtii under nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) conditions. The -P alga (55.1 μM) had a Michaelis constant (Kd) for uptake approximately one tenth of the +NP (419 μM) and -N (501 μM) cells, indicating iAs(III) uptake inhibition by extracellular phosphate. This conclusion was supported by the hyperbolic reduction in iAs(III) uptake rate (V) from 9.2 to 0.8 μmol/g-dw/h when the extracellular phosphate concentration went up from 0 to 250 μM. The maximal iAs(III) uptake rate (Vmax) of the -N alga (24.3 μmol/g-dw/h) was twice as much as that of the +NP (12 μmol/g-dw/h) and -P (8.1 μmol/g-dw/h) cells. It implies that more arsenic transporters were synthesized under the -N condition. Once accumulated, iAs(III) was oxidized and a higher proportion of arsenate (iAs(V)) was observed at lower [As]dis or under nutrient-limited conditions. Nevertheless, iAs(III) oxidation mainly occurred outside the cells with the extent of oxidation reciprocal to [As]dis. Based on the logistic modeling of the concentration-response curves in the +NP, -P, and -N toxicity tests, iAs(III) had an [As]dis-based EC50 of 1763, 13.1, and 1208 μM and an intracellular arsenic concentration based EC50 of 35.6, 28.8, and 195 μmol/g-dw, respectively. Higher iAs(III) toxicity to the -P cells occured because of their increased iAs(III) accumulation, whereas the underlying mechanisms why the -N alga was more tolerant need to be further revealed. Overall, both N and P had remarkable effects on the behavior and effects of iAs(III), which cannot be disregarded in the biogeochemical cycling research of arsenic.

Zn-bis-glutathionate is the best co-substrate of the monomeric phytochelatin synthase from the photosynthetic heavy metal-hyperaccumulator Euglena gracilis

The phytochelatin synthase from photosynthetic Euglena gracilis (EgPCS) was analyzed at the transcriptional, kinetic, functional, and phylogenetic levels. Recombinant EgPCS was a monomeric enzyme able to synthesize, in the presence of Zn(2+) or Cd(2+), phytochelatin2-phytochelatin4 (PC2-PC4) using GSH or S-methyl-GS (S-methyl-glutathione), but not γ-glutamylcysteine or PC2 as a substrate. Kinetic analysis of EgPCS firmly established a two-substrate reaction mechanism for PC2 synthesis with Km values of 14-22 mM for GSH and 1.6-2.5 μM for metal-bis-glutathionate (Me-GS2). EgPCS showed the highest Vmax and catalytic efficiency with Zn-(GS)2, and was inactivated by peroxides. The EgPCS N-terminal domain showed high similarity to that of other PCSases, in which the typical catalytic core (Cys-70, His-179 and Asp-197) was identified. In contrast, the C-terminal domain showed no similarity to other PCSases. An EgPCS mutant comprising only the N-terminal 235 amino acid residues was inactive, suggesting that the C-terminal domain is essential for activity/stability. EgPCS transcription in Euglena cells was not modified by Cd(2+), whereas its heterologous expression in ycf-1 yeast cells provided resistance to Cd(2+) stress. Phylogenetic analysis of the N-terminal domain showed that EgPCS is distant from plants and other photosynthetic organisms, suggesting that it evolved independently. Although EgPCS showed typical features of PCSases (constitutive expression; conserved N-terminal domain; kinetic mechanism), it also exhibited distinct characteristics such as preference for Zn-(GS)2 over Cd-(GS)2 as a co-substrate, a monomeric structure, and ability to solely synthesize short-chain PCs, which may be involved in conferring enhanced heavy-metal resistance.

Temporal and spatial variation of arsenic species in the Dahuofang reservoir in northeast China

Overlying water, pore water, and sediment samples were collected from the Dahuofang reservoir in November 2011 and April 2012, respectively. Total arsenic and arsenic species including arsenite, arsenate, monomethylarsonic, and dimethylarsinic were analyzed by ICP-MS and HPLC-ICP-MS. The results indicated that the environments of the Dahuofang reservoir were in reduced conditions, arsenite was the predominant species in pore water and sediments in the reservoir. Arsenic concentrations in overlying water were very low in all the samples but showed different trend during the different time. In November, arsenic concentrations in the reservoir inlet were higher than that in the other sites, whereas arsenic showed accumulation from the upstream to downstream of the reservoir in samples collected in April. In pore water, arsenic concentrations were about 23 and 37 times higher than those in overlying water in November and April, respectively, and relatively high levels of arsenite were also detected in the pore water. In surface sediments, total arsenic and arsenic species content in the reservoir inlet showed the following decreasing order: R1 > R10 > R4. The results also showed that moderate ecological risks exist in pore water and sediments in the Dahuofang reservoir.

Yeast and bacterial diversity along a transect in an acidic, As-Fe rich environment revealed by cultural approaches

Acid mine drainages (AMDs) are often thought to harbour low biodiversity, yet little is known about the diversity distribution along the drainages. Using culture-dependent approaches, the microbial diversity from the Carnoulès AMD sediment was investigated for the first time along a transect showing progressive environmental stringency decrease. In total, 20 bacterial genera were detected, highlighting a higher bacterial diversity than previously thought. Moreover, this approach led to the discovery of 16 yeast species, demonstrating for the first time the presence of this important phylogenetic group in this AMD. All in all, the location of the microbes along the transect helps to better understand their distribution in a pollution gradient.

Three-year survey of sulfate-reducing bacteria community structure in Carnoulès acid mine drainage (France), highly contaminated by arsenic

A 3-year survey on sulfate-reducing bacteria (SRB) was conducted in the waters of the arsenic-rich acid mine drainage (AMD) located at Carnoulès (France) to determine the influence of environmental parameters on their community structure. The source (S5 station) exhibited most extreme conditions with pH lowering to ~1.2; iron, sulfate, and arsenic concentrations reaching 6843, 29 593, and 638 mg L(-1), respectively. The conditions were less extreme at the downstream stations S1 (pH ~3.7; iron, sulfate, and arsenic concentrations of 1114, 4207, and 167 mg L(-1), respectively) and COWG (pH ~3.4; iron, sulfate, and arsenic concentrations of 854, 3134, and 110 mg L(-1), respectively). SRB community structures were characterized by terminal restriction fragment length polymorphism and library analyses based on dsrAB genes. The predominant dsrAB sequences detected were most similar to the family Desulfobulbaceae. Additionally, certain phylotypes could be related to spatio-temporal fluctuations of pH, iron, and arsenic species. For example, Desulfohalobiaceae-related sequences were detected at the most acidic sample (pH 1.4) with high iron and arsenic concentrations (6379 and 524 mg L(-1), respectively). New dsrAB sequences, with no isolated representatives, were found exclusively in COWG. This study gives new insights on SRB community dynamics in AMD systems.

Natural pretreatment and passive remediation of highly polluted acid mine drainage

Acid mine drainage (AMD) from the Iberian Pyrite Belt has high acidity and metal concentrations. Earlier pilot experiments, based on limestone sand dispersed in wood shavings (dispersed alkaline substrate; DAS) have been shown to be an efficient treatment option. However, complete metal removal was not achieved, principally due to the high ferrous iron concentration in the inflow AMD. In order to oxidize and remove iron, a natural Fe-oxidizing lagoon (NFOL) was added prior to treatment with limestone-DAS. The NFOL comprises several pre-existing Fe-stromatolite terraces and cascades, and a lagoon with a volume of 100 m(3) built near the mine shaft. Downstream of the NFOL, the limestone-DAS treatment consists of two reactive tanks of 3 m(3) each filled with limestone-DAS reactive substrate, connected in series with two decantation ponds of 6 m(3) each and several oxidation cascades. The AMD emerging from the mine shaft displayed a pH near 3, a net acidity of 1800 mg/L as CaCO(3) equivalents, and mean concentrations of 440 mg/L Zn; 275 mg/L Fe (99% Fe(II)); 3600 mg/L SO(4); 250 mg/L Ca; 100 mg/L Al; 15 mg/L Mn; 5 mg/L Cu; and 0.1-1 mg/L As, Pb, Cr, Cd, Co, and Ni. The oxidation induced in the NFOL enhanced ferric iron concentration, showing an average of 65% oxidation and 38% retention during the monitoring period. The whole system removed a mean of 1350 mg/L net acidity as CaCO(3) equivalents (71% of inflow); corresponding to 100% of Fe, Al, Cu, Pb and As, and 6% of Zn.

Sulfate uptake in photosynthetic Euglena gracilis. Mechanisms of regulation and contribution to cysteine homeostasis

BACKGROUND

Sulfate uptake was analyzed in photosynthetic Euglena gracilis grown in sulfate sufficient or sulfate deficient media, or under Cd(2+) exposure or Cys overload, to determine its regulatory mechanisms and contribution to Cys homeostasis.

RESULTS

In control and sulfate deficient or Cd(2+)-stressed cells, one high affinity and two low affinity sulfate transporters were revealed, which were partially inhibited by photophosphorylation and oxidative phosphorylation inhibitors and ionophores, as well as by chromate and molybdate; H(+) efflux also diminished in presence of sulfate. In both sulfate deficient and Cd(2+)-exposed cells, the activity of the sulfate transporters was significantly increased. However, the content of thiol-metabolites was lower in sulfate-deficient cells, and higher in Cd(2+)-exposed cells, in comparison to control cells. In cells incubated with external Cys, sulfate uptake was strongly inhibited correlating with 5-times increased intracellular Cys. Re-supply of sulfate to sulfate deficient cells increased the Cys, γ-glutamylcysteine and GSH pools, and to Cys-overloaded cells resulted in the consumption of previously accumulated Cys. In contrast, in Cd(2+) exposed cells none of the already elevated thiol-metabolites changed.

CONCLUSIONS

(i) Sulfate transport is an energy-dependent process; (ii) sulfate transporters are over-expressed under sulfate deficiency or Cd(2+) stress and their activity can be inhibited by high internal Cys; and (iii) sulfate uptake exerts homeostatic control of the Cys pool.

In situ proteo-metabolomics reveals metabolite secretion by the acid mine drainage bio-indicator, Euglena mutabilis

Euglena mutabilis is a photosynthetic protist found in acidic aquatic environments such as peat bogs, volcanic lakes and acid mine drainages (AMDs). Through its photosynthetic metabolism, this protist is supposed to have an important role in primary production in such oligotrophic ecosystems. Nevertheless, the exact contribution of E. mutabilis in organic matter synthesis remains unclear and no evidence of metabolite secretion by this protist has been established so far. Here we combined in situ proteo-metabolomic approaches to determine the nature of the metabolites accumulated by this protist or potentially secreted into an AMD. Our results revealed that the secreted metabolites are represented by a large number of amino acids, polyamine compounds, urea and some sugars but no fatty acids, suggesting a selective organic matter contribution in this ecosystem. Such a production may have a crucial impact on the bacterial community present on the study site, as it has been suggested previously that prokaryotes transport and recycle in situ most of the metabolites secreted by E. mutabilis. Consequently, this protist may have an indirect but important role in AMD ecosystems but also in other ecological niches often described as nitrogen-limited.

Metabolic diversity among main microorganisms inside an arsenic-rich ecosystem revealed by meta- and proteo-genomics

By their metabolic activities, microorganisms have a crucial role in the biogeochemical cycles of elements. The complete understanding of these processes requires, however, the deciphering of both the structure and the function, including synecologic interactions, of microbial communities. Using a metagenomic approach, we demonstrated here that an acid mine drainage highly contaminated with arsenic is dominated by seven bacterial strains whose genomes were reconstructed. Five of them represent yet uncultivated bacteria and include two strains belonging to a novel bacterial phylum present in some similar ecosystems, and which was named 'Candidatus Fodinabacter communificans.' Metaproteomic data unravelled several microbial capabilities expressed in situ, such as iron, sulfur and arsenic oxidation that are key mechanisms in biomineralization, or organic nutrient, amino acid and vitamin metabolism involved in synthrophic associations. A statistical analysis of genomic and proteomic data and reverse transcriptase-PCR experiments allowed us to build an integrated model of the metabolic interactions that may be of prime importance in the natural attenuation of such anthropized ecosystems.

Surface properties and intracellular speciation revealed an original adaptive mechanism to arsenic in the acid mine drainage bio-indicator Euglena mutabilis

Euglena mutabilis is a protist ubiquitously found in extreme environments such as acid mine drainages which are often rich in arsenic. The response of E. mutabilis to this metalloid was compared to that of Euglena gracilis, a protist not found in such environments. Membrane fatty acid composition, cell surface properties, arsenic accumulation kinetics, and intracellular arsenic speciation were determined. The results revealed a modification in fatty acid composition leading to an increased membrane fluidity in both Euglena species under sublethal arsenic concentrations exposure. This increased membrane fluidity correlated to an induced gliding motility observed in E. mutabilis in the presence of this metalloid but did not affect the flagellar dependent motility of E. gracilis. Moreover, when compared to E. gracilis, E. mutabilis showed highly hydrophobic cell surface properties and a higher tolerance to water-soluble arsenical compounds but not to hydrophobic ones. Finally, E. mutabilis showed a lower accumulation of total arsenic in the intracellular compartment and an absence of arsenic methylated species in contrast to E. gracilis. Taken together, our results revealed the existence of a specific arsenical response of E. mutabilis that may play a role in its hypertolerance to this toxic metalloid.

Characterization of the active bacterial community involved in natural attenuation processes in arsenic-rich creek sediments

Acid mine drainage of the Carnoulès mine (France) is characterized by acid waters containing high concentrations of arsenic and iron. In the first 30 m along the Reigous, a small creek draining the site, more than 38% of the dissolved arsenic was removed by co-precipitation with Fe(III), in agreement with previous studies, which suggest a role of microbial activities in the co-precipitation of As(III) and As(V) with Fe(III) and sulfate. To investigate how this particular ecosystem functions, the bacterial community was characterized in water and sediments by 16S rRNA encoding gene library analysis. Based on the results obtained using a metaproteomic approach on sediments combined with high-sensitivity HPLC-chip spectrometry, several GroEL orthologs expressed by the community were characterized, and the active members of the prokaryotic community inhabiting the creek sediments were identified. Many of these bacteria are β-proteobacteria such as Gallionella and Thiomonas, but γ-proteobacteria such as Acidithiobacillus ferrooxidans and α-proteobacteria such as Acidiphilium, Actinobacteria, and Firmicutes were also detected.

Using meiofauna to assess pollutants in freshwater sediments: a microcosm study with cadmium

The direct and indirect effects of Cd on benthic communities were assessed in a freshwater microcosm study over a period of seven months (218 d). Cadmium was regarded as a model substance to evaluate the usefulness of small-scale laboratory microcosm with microscopic fauna. In particular, effects on the meiofauna community, an ecologically important but rather neglected benthic component, were investigated. In addition, some microfaunal parameters (protozoan abundance and microbial activity) were determined. The sediment was spiked with nominal Cd concentrations of 10, 100, and 1,000 mg/kg dry weight. Because of the strong binding of Cd to sediment particles, measured Cd pore-water concentrations never exceeded 129.5 ± 40.7 µg/L. At 1,000 mg/kg dry weight, the abundances of the two dominant meiofauna taxa, nematodes and oligochaetes, were significantly reduced throughout the present study. Regarding nematodes, species of bacterivorous taxa (Daptonema, Eumonhystera) decreased, whereas species of predacious and omnivorous taxa (Mononchus, Dorylaimus, and Ironus) increased in dominance in microcosms of the highest Cd concentration. Transient effects on microfauna were observed, especially in the first half of the present study, with a reduction in microbial activity and protozoan abundance. However, in microcosms receiving the highest Cd concentration, the abundance of the flagellate Euglena mutabilis increased significantly toward the end of the present study. The results of the present study support the use of small-scale microcosms with natural meiofauna communities as a suitable tool to assess the impact of pollutants in freshwater sediments.

Increased synthesis of α-tocopherol, paramylon and tyrosine by Euglena gracilis under conditions of high biomass production

AIMS

To analyse the production of different metabolites by dark-grown Euglena gracilis under conditions found to render high cell growth.

METHODS AND RESULTS

  The combination of glutamate (5 g l(-1) ), malate (2 g l(-1) ) and ethanol (10 ml l(-1) ) (GM + EtOH); glutamate (7·15 g l(-1) ) and ethanol (10 ml l(-1) ); or malate (8·16 g l(-1) ), glucose (10·6 g l(-1) ) and NH(4) Cl (1·8 g l(-1) ) as carbon and nitrogen sources, promoted an increase of 5·6, 3·7 and 2·6-fold, respectively, in biomass concentration in comparison with glutamate and malate (GM). In turn, the production of α-tocopherol after 120 h identified by LC-MS was 3·7 ± 0·2, 2·4 ± 0·1 and 2 ± 0·1 mg [g dry weight (DW)](-1) , respectively, while in the control medium (GM) it was 0·72 ± 0·1 mg (g DW)(-1) . For paramylon synthesis, the addition of EtOH or glucose induced a higher production. Amino acids were assayed by RP-HPLC; Tyr a tocopherol precursor and Ala an amino acid with antioxidant activity were the amino acids synthesized at higher concentration.

CONCLUSIONS

Dark-grown E. gracilis Z is a suitable source for the generation of the biotechnologically relevant metabolites tyrosine, α-tocopherol and paramylon.

SIGNIFICANCE AND IMPACT OF THE STUDY

By combining different carbon and nitrogen sources and inducing a tolerable stress to the cell by adding ethanol, it was possible to increase the production of biomass, paramylon, α-tocopherol and some amino acids. The concentrations of α-tocopherol achieved in this study are higher than others reported previously for Euglena, plant and algal systems. This work helps to understand the effect of different carbon sources on the synthesis of bio-molecules by E. gracilis and can be used as a basis for future works to improve the production of different metabolites of biotechnological importance by this organism.

Speciation of arsenic in Euglena gracilis cells exposed to As(V)

Euglena gracilis is a photosynthetic eukaryote ubiquitous in arsenic-polluted acid mine drainages and is locally exposed to As(III) and As(V) concentrations up to 250 and 100 mg L(-1), respectively. Here, arsenic speciation in E. graciliswas determined by X-ray absorption spectroscopy and selected (bio)chemical methods on cells grown at nonlimiting phosphate concentrations. Our results suggest the following detoxification scheme: (1) uptake of As(V) from solution in competition with phosphate, (2) intracellular reduction to As(III), (3) complexation by cytoplasmic proteic thiol ligands of low molecular weight, and (4) As(III) export from the cell. However, at As(V) concentrations >100 mg L(-1), growth rate is markedly lowered and As(V) remains mostly unreduced during the extended lag period. Intracellular As(V) is found to be exclusively concentrated in the membrane + nucleus fraction, suggesting that arsenate could substitute for phosphate groups in membranes or in phosphate-containing macromolecules. Thus, arsenic species are partitioned, with As(III)-thiol compounds concentrated in the cytoplasmic proteic pool and As(V)-compounds associated with the membrane + nucleus fraction. The increasing growth delay observed with increasing initial As(V) concentration in the culture medium is proposed to result from the combination of a higher As(V) uptake and limiting intracellular As(V) reduction rate and As(III) export rate. Under high As(V) exposure conditions (200 mg L(-1)) the reduction step is found to be the most limiting step for detoxification.

Isolation and diversity analysis of arsenite-resistant bacteria in communities enriched from deep-sea sediments of the Southwest Indian Ocean Ridge

Microorganisms play an important role in the geobiocycling of arsenic element. However, little is known about the bacteria involved in this process in oceanic environments. In this report, arsenite-resistant bacteria were detected in deep-sea sediments on the Southwest Indian Ridge. From arsenite enriched cultures, 54 isolates were obtained, which showed varied tolerance to arsenite of 2-80 mM. Phylogenetic analysis based on 16S rRNA showed that they mainly belonged to Proteobacteria and Actinobacteria. Denaturing gradient gel electrophoresis revealed that Microbacterium esteraromaticum was the dominant member in the arsenite enriched communities, and this was reconfirmed by 16S rRNA gene library analyses. Thus, M. esteraromaticum showed highest resistant to arsenite among the detected bacteria. These results indicate that there are quite diverse bacteria of arsenite resistance inhabiting the deep sea sediment, which may play a role in the geobiocycling of arsenic element in marine environments.

XAS study of arsenic coordination in Euglena gracilis exposed to arsenite

Among the few eukaryotes adapted to the extreme conditions prevailing in acid mine drainage, Euglenae are ubiquitous in these metal(loid)-impacted environments, where they can be exposed to As(III) concentrations up to a few hundreds of mg x L(-1). In order to evaluate their resistance to this toxic metalloid and to identify associated detoxification mechanisms, we investigated arsenic coordination in the model photosynthetic protozoan, Euglena gracilis, cultured at pH 3.2 and exposed to As(III) at concentrations ranging from 10 to 500 mg x L(-1). E. gracilis is shown to tolerate As(III) concentrations up to 200 mg * L(-1), without accumulating this metalloid. X-ray absorption spectroscopy at the As K-edge shows that, in the cells, arsenic mainly binds to sulfur ligands, likely in the form of arsenic-trisglutathione (As-(GS)3) or arsenic-phytochelatin (As-PC) complexes, and to a much lesser extent to carbon ligands, presumably in the form of methylated As(III)-compounds. The key role of the glutathione pathway in As(III) detoxification is confirmed by the lower growth rate of E. gracilis cultures exposed to arsenic, in the presence of buthionine sulfoximine, an inhibitor of glutathione synthesis. This study provides the first investigation at the molecular scale of intracellular arsenic speciation in E. gracilis and thus contributes to the understanding of arsenic detoxification mechanisms in a eukaryotic microorganism under extreme acid mine drainage conditions.

Enhanced alternative oxidase and antioxidant enzymes under Cd2+ stress in Euglena

To identify some of the mechanisms involved in the high resistance to Cd(2+) in the protist Euglena gracilis, we studied the effect of Cd(2+) exposure on its energy and oxidative stress metabolism as well as on essential heavy metals homeostasis. In E. gracilis heterotrophic cells, as in other organisms, CdCl(2) (50 microM) induced diminution in cell growth, severe oxidative stress accompanied by increased antioxidant enzyme activity and strong perturbation of the heavy metal homeostasis. However, Cd(2+) exposure did not substantially modify the cellular respiratory rate or ATP intracellular level, although the activities of respiratory complexes III and IV were strongly decreased. In contrast, an enhanced capacity of the alternative oxidase (AOX) in both intact cells and isolated mitochondria was determined under Cd(2+) stress; in fact, AOX activity accounted for 69-91% of total respiration. Western blotting also revealed an increased AOX content in mitochondria from Cd(2+)-exposed cells. Moreover, AOX was more resistant to Cd(2+) inhibition than cytochrome c oxidase in mitochondria from control and Cd(2+)-exposed cells. Therefore, an enhanced AOX seems to be a relevant component of the resistance mechanism developed by E. gracilis against Cd(2+)-stress, in addition to the usual increased antioxidant enzyme activity, that enabled cells to maintain a relatively unaltered the energy status.

Molecular mechanisms of resistance to heavy metals in the protist Euglena gracilis

The biochemical mechanisms of resistance to several heavy metals, which are associated with their accumulation (binding by high-affinity chelating molecules such as thiol-compounds together with their compartmentalization into organelles), are analyzed for the photosynthetic, free-living protist Euglena gracilis. The complete understanding of these mechanisms may facilitate the rational design of strategies for bioremediation of heavy metal polluted water and soil systems.

Current perspectives in analyte extraction strategies for tin and arsenic speciation

Nowadays, reliable and robust detectors can be considered standard laboratory instrumentation, which, for most of the elements provide quantitation limits in the lower ng/g range. Despite these advances in detector technology, sample preparation is by far the most important error source in modern analytical method development and can be judged as the "Achilles' heel" of any analytical process regarding reliability of the obtained results and time consumption. The aim of the present review is to highlight modern trends for tin and arsenic speciation, as these analytes can be considered as models for challenges in modern method development in this field. First background information, legislative aspects and current needs are elucidated. Then the role of sample treatment within the process of method development in speciation is discussed, followed by a presentation of modern extraction techniques, matching the requirements for arsenic and tin speciation analysis: to provide mild conditions in order to ensure species preservation, to improve species recovery, to enhance sample throughput and to be suitable for hyphenation with chromatographic separation systems. The review includes applications on tin and arsenic speciation, covering the period of 2001-2006.

Diel cycles of arsenic speciation due to photooxidation in acid mine drainage from the Iberian Pyrite Belt (Sw Spain)

Twenty four hours diel cycles of arsenic speciation in Acid Mine Drainage (AMD) due to photooxidation have been reported for the first time. AMD samples were taken during 48 h (31st March and 1st April, 2005) at 6 h intervals from the effluent of a massive abandoned polymetallic sulphide mine of the Iberian Pyrite Belt (Sw Spain). Samples were preserved in situ using cationic exchange prior to analysis by coupled high performance liquid chromatography, hydride generation and atomic fluorescence spectrometry (HPLC-HG-AFS) for arsenic speciation. The results indicated the presence of inorganic arsenic species with daily means of 262mugl(-1) for As(V) and 107 microg l(-1) for As(III). No marked diel trend was observed for As(V). However, a marked diel trend was observed for As(III) in the two studied days, with maximum concentrations during nighttime (141-143 microg l(-1)) and minimum concentrations at daytime (72-77 microg l(-1)). This difference in concentration during daytime and nighttime is ca. 100%. A similar diel cycle was observed for iron. An explanation for the arsenic diel cycles observed is the light induced photooxidation of As(III) and the elimination of As(V) due to its adsorption onto Fe precipitates during the daytime. Furthermore, the diel changes in arsenic speciation emphasize the importance of designing suitable sampling strategies in AMD systems.

Diversity of microorganisms in Fe-As-rich acid mine drainage waters of Carnoulès, France

The acid waters (pH 2.7 to 3.4) originating from the Carnoulès mine tailings contain high concentrations of dissolved arsenic (80 to 350 mg.liter(-1)), iron (750 to 2,700 mg.liter(-1)), and sulfate (2,000 to 7,500 mg.liter(-1)). During the first 30 m of downflow in Reigous creek issuing from the mine tailings, 20 to 60% of the dissolved arsenic is removed by coprecipitation with Fe(III). The microbial communities along the creek have been characterized using terminal-restriction fragment length polymorphism (T-RFLP) and 16S rRNA gene library analyses. The results indicate a low bacterial diversity in comparison with unpolluted water. Eighty percent of the sequences obtained are related to sequences from uncultured, newly described organisms or recently associated with acid mine drainage. As expected owing to the water chemistry, the sequences recovered are mainly related to bacteria involved in the geochemical Fe and S cycles. Among them, sequences related to uncultured TrefC4 affiliated with Gallionella ferruginea, a neutrophilic Fe-oxidizing bacterium, are dominant. The description of the bacterial community structure and its dynamics lead to a better understanding of the natural remediation processes occurring at this site.